In a fuel cell mode of electrochemical conversion, an organic fuel such as a hydrocarbon or an oxygen-containing organic compound (e.g., an alcohol, aldehyde, ketone, ether or ester) is directly converted into electrical energy and simultaneously oxidized in various stages to carbon dioxide. Such fuel cells include an anode or fuel electrode, a cathode or oxygen electrode, respective supplies of an organic fuel, an oxidizing agent consisting of, or containing, molecular oxygen, and an aqueous electrolyte in which the electrodes are immersed. With the use of an alkaline electrolyte, oxygen is reacted with the aqueous electrolyte solution to form negatively charged ions at the cathode, fuel is oxidized at the anode, and free electrons are released upon a conducting surface of the anode. When an acidic electrolyte is utilized, hydrogen ions formed at the anode migrate to the cathode where water is formed. When current is drawn from the cell, there is a net flow of electrons from the anode through an external circuit to the cathode.
During this direct conversion of the chemical energy of the hydrocarbon fuel to electrical energy, the fuel is oxidized in various stages until it has been converted into carbon dioxide. Carbon dioxide is the anodic compartment effluent when a fuel cell is operating in a conventional manner, and the primary objective is the production of electrical energy.
There has been increasing interest in the potential use of electrogenerative processes for the production of oxygenated organic compounds from a feed source that has a lower state of oxidation than the oxygenated conversion products, concomitant with the generation of electrical energy. With respect to a fuel cell, the oxygenated conversion products would represent an oxidation state in an intermediate oxidation range between the starting material and carbon dioxide.
U.S. Pat. No. 3,245,890 describes an electrochemical process for simultaneous production of carbonyl compounds and electrical energy with a system of separate anodic and cathodic zones. The anodic zone contains an acidic aqueous solution of a platinum group metal halide. Olefin feed is introduced into the anodic zone, and an oxidizing agent is introduced into the cathodic zone. Butene-1 converts to methyl ethyl ketone product. The metal halide functions as an oxidizing agent, and is in turn re-oxidized at the anodic electrode.
U.S. Pat. No. 3,280,014 describes a fuel cell operation in which an alcohol is oxidized to a carbonyl compound at the fuel electrode, such as the conversion of benzyl alcohol to benzaldehyde. The dehydrogenation of cyclic hydrocarbons to aromatic hydrocarbons is also disclosed. Both electrodes are constructed of activated porous carbon.
U.S. Pat. No. 3,316,161 describes a multi-stage fuel cell system for partially oxidizing an alcohol feed stepwise to different levels of oxidation to carbonyl and carboxylic acid compounds.
U.S. Pat. No. 3,329,593 describes a continuous process in which a C.sub.4 hydrocarbon mixture of isobutylene, n-butylenes and butanes is contacted with a first aqueous sulfuric acid solution to extract the isobutylenes, and the mixture is contacted with a second aqueous sulfuric acid solution to extract the n-butylenes. The acidic n-butylene extract phase is contacted with a fuel electrode to convert n-butylene to methyl ethyl ketone, and the residual butane fraction from the previous extraction cycles is used to extract the methyl ethyl ketone from the anolytic medium.
U.S. Pat. No. 4,347,109 describes a method of producing acetaldehyde which involves passing gaseous ethanol in contact with a gas-permeable fluid-impermeable fuel electrode, and recovering acetaldehyde as a component of the gas phase effluent from the anodic compartment.
There remains a need for the development of efficient electrogenerative systems for the production of value-added organic chemicals for inexpensive feedstocks.
Accordingly, it is an object of this invention to provide an improved electrochemical system for electrogenerative partial oxidation of hydrocarbon feedstock.
It is another object of this invention to provide an electrogenerative process for converting hydrocarbons to partially oxidized products with a high current efficiency.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.